In vehicles, in particular in road vehicles, there is a need to supply clean air to a vehicle interior, preferably a passenger compartment. The air supply for the vehicle interior usually takes place with the aid of an air conditioning system, which sucks in air from the interior, cleans it with the aid of an interior air filter, and returns it to the interior (recirculating air mode), or sucks in fresh air from the environment, cleans it with the aid of the interior air filter, and supplies it to the interior (fresh air mode). Likewise, in the case of modern air conditioning systems, any number of intermediate settings between such a recirculation mode and such a fresh air mode are possible (mixed air mode). While such an interior air filter originally only had to filter out coarse impurities from the air, the requirements for such interior air filters and the filter materials thereby used have constantly increased. Meanwhile, with the aid of an interior air filter, a purification of the sucked-in air from pollen, fine dust and odours is to be achieved. In particular, the removal of odours from the sucked-in air presents difficulties, since different odorous substances also require different filter materials. However, if a corresponding number of different filter materials are required for an increasing number of different odorous substances, the flow resistance of the air filter increases, which impedes economical operation of the air conditioning system. Multilayer filter materials are therefore preferably used; these always represent an optimised compromise for the respective cleaning task. If such an air filter can filter out both particulate impurities, i.e. solid and/or liquid impurities, as well as gaseous impurities from the air, such an air filter is frequently also referred to as a hybrid filter. Such hybrid filter are often specified by means of requirement specifications, which generally take into account the following gases: n-butane, toluene, sulphur dioxide, nitrogen oxides, ozone. These hybrid filters are, for example, specified in accordance with ISO standard 11155 part 2. This standard specification, however, represents odour loads that were determined in European urban centres about 30 years ago. Today's external air conditions, such as those available in the urban areas of Europe and especially in Asia, differ from these earlier external air conditions. For example, the environmental air nowadays can contain amines and aldehydes that transport odours, and which cannot be filtered, or only inadequately, by the above-mentioned hybrid filters in accordance with the standard specification.
A filter element with a multilayer filter material is of known art from DE 10 2005 016 677 A1, in which an active layer with activated carbon fibres is provided, which is arranged on the inflow side, which is followed by an adsorber layer with granular adsorbents on the outflow side. A further active layer with activated carbon fibres can adjoin this adsorber layer on the outflow side. The adsorbents used here can comprise activated carbon, zeolites, cyclodextrins, silicates, ion exchangers and aluminosilicates.
DE 10 2012 007 503 A1 discloses another adsorptive filter medium, in which a plurality of first filter layers are provided with a first adsorption substance and a plurality of second filter layers differing from the first filter layers are provided with a second adsorption substance; these alternate with one another and have differing flow resistances or pressure losses.
A further adsorptive filter material is of known art from DE 10 2009 021 020 A1 and contains an exchange resin that is loaded with metal cations.